Aged GM-CSF/IL-3–deficient mice develop fasting hyperglycemia. Blood sugar levels were determined for wild-type (n = 30), GM-CSF−/− (n = 10), IL-3−/− (n = 8), and GM-CSF/IL-3−/− (n = 30) mice. Of 30 GM-CSF/IL-3 doubly deficient mice, 22 showed fasting hyperglycemia compared with control mice (P < .001, Wilcoxon rank sum test).